Molecular Mechanisms Underlying Innate Immune Kinase TBK1-Driven Oncogenic Transformation

An essential kinase in innate immune signaling, TBK1 couples pathogen surveillance to induction of host defense mechanisms. The pathological activation of TBK1 in cancer can overcome programmed cell death cues, enabling cells to survive oncogenic stress. The mechanistic basis of TBK1 prosurvival signaling, however, has been enigmatic. Here we show that TBK1 directly activates AKT by phosphorylation of the canonical activation loop and hydrophobic motif sites independently of PDK1 and mTORC2. A population of AKT is bound to components of the exocyst complex. Upon mitogen stimulation, triggering of the innate immune response, re-exposure to glucose, or oncogene activation, TBK1 is recruited to the exocyst, where it activates AKT. In cells lacking TBK1, insulin activates AKT normally, but AKT activation by these exocyst-dependent mechanisms is impaired. Discovery and characterization of a 6-aminopyrazolopyrimidine derivative, as a selective low nanomolar TBK1 inhibitor, indicates this regulatory arm can be pharmacologically perturbed independently of canonical PI3K/PDK1 signaling. Thus, AKT is a direct TBK1 substrate that connects TBK1 to prosurvival signaling. Additionally, biochemical and cell biological evidence indicates critical roles of TBK1 and its analog IKKε in the amino acid-dependent activation of mTORC1. TBK1 and IKKε are activated by amino acids and both proteins interact with mTORC1. In TBK1 and/or IKKε-deficient cells, mTORC1 activation by amino acids is impaired. Of note, we also discovered a set of TBK1 substrates and interacting proteins participating in amino acid-dependent mTORC1 signaling. In conclusion, our results suggest that TBK1 not only supports physiological and oncogenic activation of AKT, but also plays a central role in the regulation of mTORC1 activation in response to amino acids. In addition, our studies reveal novel mTORC1 components and provide new insights into the regulation of the mTORC1 signaling network.